Antistatic code paper

ABSTRACT

Code paper, suitable for use for punch-coding purposes, is produced by an improved process which includes sizing paper made of chemical wood pulp with a surface applied size press treatment containing an inorganic salt on a paper machine. The addition of the inorganic salt to the size press formulation has no deleterious effect on the physical properties of the paper produced and even when applied in very small quantities, produces a large decrease in the tendency of the paper to accept and retain a static charge.

United States Patent DeMatte Sept. 2, 1975 [5 1 ANTISTATIC CODE PAPER 3,480,455 11 1969 Richardson 117/156 3,536,578 10/1970 Brundige 162/184 [75] Inventor Michael Columbla, 3,637,407 1 1972 Schobinger et a1.. 106/213 [73] Assignee: westvaco Corporation, New York, 3,702,801 11/1972 DeMatte 162 173 N.Y. Primary ExaminerS. Leon Bashore [22] Ffled: 1973 Assistant ExaminerPeter Chin [21] Appl. No.: 406,888

[57] ABSTRACT 521 US. Cl. 162/173; 106/213; 162/175; Code Paper Suitable for use for Punch-Coding 162/l8l 162/184 poses, is produced by an improved process which in- [51] Int. C1. D 2lD 3/00 dudes Sizing paper made of Chemical wood pulp with f Search l I I u A a surface size press treatment containing an 162/184;1O6/213; 1 /1 56 inorganic salt on a paper machine. The addition of the inorganic salt to the size press formulation has no del- [56] References Cited eterious effect on the physical properties of the paper produced and even when applied in very small quanti- UNITED STATES PATENTS ties, produces a large decrease in the tendency of the paper to accept and retain a static charge. ay or 3,328,184 6/1967 Wcber 117/156 5 Claims, N0 Drawings ANTISTATIC CODE PAPER BACKGROUND OF INVENTION Code paper is paper designed to be converted into perforated tape, the punched tape used in teletype machines, computers, automatic type setting systems, and various date processing systems. In general, code paper is made entirely from chemical wood pulp which is free of fillers and abrasive particles. The paper may also contain a small amount of a lubricant such as oil or it may be oiled in an off-machine process by the converter for better lubricating properties, and reduced punch wear.

The paper is converted into tapes by slitting it into widths ranging from about one-half inch to three inches, the most frequently used tape widths being in the order of 0.685, 0.875 and 1.0 inch.

In use, letters, numbers, punctuation and certain machine-function instructions are represented on the code paper tape by a code consisting of holes punched across the tape. The small piece of paper which is removed by the punch in the punch-coding process is called a chad. The holes are placed in the tape by a tape punch or perforator which is usually an electromechanical device which uses pins to punch data on the tape. Some punches are activated by a keyboard, some by electrical impulses from another machine such as a computer or data transmission device, and others are activated by both means. The codes placed on the tape employ various hole/no-hole combinations in channels which may range in number from 5 to 8. In addition to the code holes across the tape, the tape usually carries feed holes so that in a five-channel code for example a fully punched tape would have three code holes, a feed hole, and two more code holes centered on a line perpendicular to the lengthwise direction of the tape.

In order to avoid excessive wear of the punches, code paper is often treated with a lubricating oil as mentioned hereinbefore. The oil may be applied to the paper by the convertor in an offmachine process, but preferably the oil is applied as taught by the applicants prior U.S. Pat. No. 3,702,801 in which an oil-in-water emulsion is added at the size press. I

Notwithstanding the above, however, oiled code paper as well as standard non-oiled code paper is often subject to problems arising from static build-up on the surface of the paper during the dry winter months.

The excessive build-up of static charges on the tape or code paper affects the punching or perforating operations to such an extent that the punched out paper or chads do not become permanently disassociated from the tapes or paper, but tend to be attracted to and adhere to the tapes or paper in random fashion, thus giving rise to a complete or at least partial blockage of the perforations or punched out holes. And, of course, the tapes which are affected as noted above are prone to produce errors in the read-out machines which utilize the tapes because of the presence of complete or partially-blocked holes. In some cases, the use of mechanical means such as brushes or pneumatic devices such as air jets have been employed to remove the punched out paper or chads from the punched tapes but this solution has not been completely reliable.

Accordingly, the subject invention resides in the discovery that the addition of a small amount of an inorganic salt, in a surface size press treatment to code paper during the paper making process, will eliminate altogether the build-up of static electricity charges on the tapes prepared from the code paper during the punching and perforating operation. Moreover, the subject invention achieves its objective without leaving a residual grit in the paper or otherwise producing any other deleterious effect on the physical properties of the paper including its lubricity where the inorganic salt is incorporated in the production of code paper containing oil.

The build-up of static charges on paper, particularly under low moisture conditions, i.e., during the winter months where relative humidity is low, is understandable since paper is a good dielectric. Accordingly, efforts to eliminate these static charges have been attempted by many people but with not completely satisfactory results for various reasons. For instance, in an effort to reduce the amount of static build-up on the surface of the paper by the internal dissipation of the charge, US Pat. No. 3,535,155 describes a process which utilizes the addition of small amounts of iron soaps or organic carboxylic acids, and optionally with small amounts of petroleum sulfonic acid alkali or alkaline earth metal salts to the paper. However, the process described in the aforementioned patent is undesirable since it is in the form of an off-machine process. In other instances, some organic salts in the form of ashless organic antistatic agents are known to be effective in eliminating static build-up on paper, however the known additives are plagued by poor efficiency, i.e., a large quantity is necessary for gm d results, and also because of their exhorbitant expense. Consequently, the utilization of organic antistatic agents is avoided if possible.

Subsequently, the use of an inorganic salt in the code paper for the purpose of reducing the static electricity build-up was considered, but it was rejected at first since it was known that inorganic salts function as humectants at high RH and it was suspected that the use of inorganic salts would leave a grit or ash in the paper that would be prohibitive to punch wear. However, later experiments proved otherwise.

SUMMARY OF INVENTION When inorganic salts were employed at the size press in small quantities during the production of code paper, a substantial decrease in the tendency of the paper produced to accept and retain a static charge was observed. This unexpected result was achieved even at very low humidities with a variety of different salts, and without any deleterious effect to the physical properties or performance of the paper. Accordingly, it was postulated that the addition of the inorganic salt on machine, at the size press, while the sheet was not completely dried and fiber-to-fiber bonding was incomplete, permitted the ionic species to become bonded between the fibers with the result that it would conduct away the static charge after complete sheet formation.

According to the present invention, a dispersion of starch in water is first prepared. Then under agitation and in the presence of heat, an inorganic salt is added to the dispersion. The dispersion thus produced is subsequently applied to the base paper web by any suitable means such as dipping, spraying or brushing, but preferably is applied by means of a size press or a paperma chine to produce a reliable antistatic code paper. In the case where the code paper is desired to have improved lubrieity, an emulsifier and a lubricating oil are also added to the dispersion to form an oil-in-water emulsion substantially as disclosed in applicants prior U.S. patent referred to hereinbefore. After the paper is impregnated with either the starch/salt dispersion or the oii-in-water/starch/salt dispersion at the size press, it is dried to a moisture content of about 4 to 8 7c and slit into the required dimensions for code paper tapes.

The invention is not limited to the use of a particular type of starch in the sizing. Pearl, acid modified, cationic, oxidized and ethylated starches can be used in the sizing, with the preferred being a pearl corn starch. The amount of starch in the size press formulation can be varied from about 1.5 to 15% by weight, with the preferred being about to 10% by weight. Above about starch by weight, the formulation becomes too viscous for easy handling, especially with pearl corn starch, and below 1.5% starch by weight the emulsion becomes unstable and not suitable for size press application.

Where a pro-lubricated antistatic code paper is produced, the oil used may be one of any of the well known liquid lubricating oils, including motor oils, paraffinbased oils, and mineral oils. The amount of oil used in the emulsion is quite small, ranging from about 1 to 10%, and preferably from about 3 to 5% by weight of the total emulsion including starch, water, emulsifier and oil. The emulsifiers used in making the prelubricated antistatic code paper may be of any of those commercially available and particularly an emulsifier known as Tween 80, a polyoxyethylene sorbitan monooleate, or, Tegitol-NP27, a nonyl phenylethylene glycol ether.

In addition, the invention is not limited to the use of any particular type of inorganic salt in the sizing. Acid salts, basic salts and neutral salts would each perform satisfactorily in the present invention with salts from the group consisting of ammonium chloride, potassium chloride and sodium chloride being preferred. in those cases where the code paper has a maxium chloride ion specification, salts from the group consisting of potassium sulfate or potassium nitrate could be substituted.

The base paper used for the purpose of the present invention has been referred to as paper made wholly from chemical wood pulp. As those skilled in the art will readily appreciate. chemical wood pulp is obtained by digestion of wood with various cooking solutions and includes pulp prepared by the known sulfate (or Kraft process), sulfite and neutral sulfite semichemical processes. Mechanical pulp, commonly called groundwood, is not suitable for use in producing the technical grade of paper known as code paper. The chemical wood pulp used herein is preferably bleached to produce a white pulp.

Accordingly, the addition of an inorganic salt and the concomittant result in the decrease in static charge build-up provides an increase in the efficiency of the coding operation on the code paper tapes since there is no more chad flocculation nor any other undesirable problems normally associated with static electricity.

DETAILED DESCRIPTION The conversion of code paper into a perforated tape requires a punching operation. The mechanics of punching well as the overall encoding operation creates a substantial amount of static charge on the coded paper tapes produced. However, in accordance with the present invention, it has been found that the static charge buildup can be substantially reduced or eliminated entirely with the application of an inorganic salt to the paper. The process of the present invention consists of the addition of a small amount of an inorganic salt such as ammonium chloride, potassium chloride or sodium chloride in a surface sizing application on the paper machine during the process of making the paper. The quantity of the inorganic salt added to the code paper is controlled by the size press conditions, concentration at the size press and the sizepress solution pickup. On the other hand, the invention has also been found to be effective in reducing the tendency of paper to hold a surface static charge using an off-machine size press application.

It was thus found quite surprising that a very small quantity of salt when applied at the size press would effectively eliminate the static charge on paper. Concentrations as low as 0.3% by weight of salt when applied at the size press under mill conditions, produced paper having very good antistatic properties without inhibiting the lubricity or other physical properties of the paper. The determinative factor in measuring the antistatic performance of the paper was related to the time required for the paper to dissipate a charge applied thereto. Of course, the quicker the charge was dissipated, the better the antistatic properties of the paper, and, this time period was graphically represented with the use of electrometer tracings as more fully described hereinafter.

Thus it is believed that the process according to the present invention is useful because the addition of the inorganic salt at a size press with the web in either a not completely formed state, or in a wetted state, permits the salt to become attached to, or bonded between the paper fibers thus insuring the efficient use of the ionic species to conduct static charge.

EXAMPLE 1 As a first step in testing the hypothesis of the present invention, an unsized web of paper prepared from chemical wood pulp and having a basic weight of 50 pounds per ream, i.e., the weight of 500 sheets, 25 X 38 inches, was used as a basestock. For the control, an aqueous dispersion of pearl starch was prepared in a batch process by cooking 6 grams of starch in grams of water at a temperature of from l8()l90 F. for about 20 minutes to produce a 6 7c by weight dispersion of starch. Later on, other sizepress solutions were prepared in substantially the same manner except with the addition of increasing amounts of ammonium chloride (NH CI) from l to 671 by weight. The different sizepress solutions were then applied to the basestock on a laboratory size press and after the traveling web was impregnated with the dispersion, the web was dried to about 6% moisture content and cut into sheets for testing. An analysis of the paper so produced showed that the total size press pickup of starch and salt was from 0.8 to L6 lb/ream. The antistatic properties of the sheets prepared were then measured with the use of electrometer curves at a relative humidity of 16% (plus or minus 171 The electronieter curves were obtained by applying a test corona voltage to the sheet for 3 seconds during which time the sheets accepted a charge. After charging. measurements were then taken of the charge dissipation with time and the charge dissipation was recorded photographically so as to produce a curve. The technique used is one that is well known and accepted in the industry as a measure of the ability of a sheet of paper to accept and dissipate a charge. The results of the tests are shown in Table I.

In each of the conditions of Example I, the time of decay readings were obtained by averaging several samples with the final reading being around 50 volts, and for the two final conditions (5 and 6% Nl-l Cl), the charge dissipation after only 1 second was about 100 volts. Thus it may be postulated that paper has good or acceptable antistatic properties for use as code paper where the charge applied to the paper is dissipated, or reduced to about 50 volts in less than about 10 seconds. Furthermore, it may be seen that with increasing amounts of inorganic salt added to the size press, the charge decaying properties of the sheet became increasingly more efficient. It may also be noted that with increasing amounts of salt in the size press, the charge acceptance of the sheet was reduced slightly.

EXAMPLE II A second experiment similar to Example I was conducted using an unsized basestock, except that a lubricating oil was added to the sizepress solution substantially as disclosed in applicants prior U.S. Pat. No. 3,702,801. Control sheets were prepared with a sizepress solution containing by weight 94 grams water, 6 grams starch and 4 grams of Faxam 40 lubricating oil. A small amount of an emulsifier, TergitoI-NP27 was also added to the solution and the solution was cooled at l8()l9() F. for about minutes under agitation. Similar sizepress solutions were then prepared but with the addition of increasing amounts of the inorganic salt ammonium chloride (NZ ,Cl). Sheets were prepared from the paper so treated and electrometer tracings substantially as described in connection with Example l were prepared with the following results.

TABLE II Sizeprcss Solution Containing 6 "/1 Pearl X Starch and 4 /1 Faxam 40 Lubricating Oil From the results of Example II, it may be seen that the addition of salt to the oil-inwater emulsion described in applicants prior US. Patent strongly influences the dissipation of the charge applied to the paper. In each instance, the total pickup at the size press ranged from 0.5 to l.5 lb./ream. Once again, for the 5 and 6% NH,Cl size press solutions the decrease in charge was substantially instantaneous, with the same samples also showing a tendency to accept a lesser initial charge. The paper sized with the 3 and 4% NH,CI solutions also showed good performance and based on the two examples reproduced above, the hypothesis of the invention was substantially proved in the laboratory wherein the salt was believed to become attached to the paper fibers through a chemical mechanism.

However, in order to check the physical properties of the paper treated with salt, a series of physical tests were performed on the samples containing 4 and 5 NH CI and on the control sample.

EXAMPLE III The physical properties and lubricity of the paper samples prepared using the 4 and 5% Nl-LCI solutions in Example II were checked and compared with similar physical properties of the control sheets in an effort to see in any deleterious effects were produced by practicing the present invention. For this purpose, conventional TAPPI Standard tests were performed on the paper samples to determine the Burst, Tear, Fold and Tensile strength of the sheets. In addition, the lubricity of the sheets was measured using the Stanley Knife test. In this latter test, a number of sheets in pad form are subjected to a series of ten cuts, and the final sheet penetrated by at least three of the ten cuts is taken as a measure of the lubricity of the sheets. For each of the TAPPI Standard tests, the samples were each tested with the sheets oriented in the machine direction (MD). The results are tabulated below.

TABLE III Size press solution 6 Pearl X Starch 4 Faxam 4O Lubricating oil and Emulsifier (Tergitol NP-Z'l) Thus it may be seen from the data in Table III that with the addition of salt to the size press solution the tear was only slightly reduced with the readings for fold, tensile, Burst and lubricity remaining nearly the same.

In a final set of laboratory experiments, several different sizepress solutions were prepared using different inorganic salt materials. Basically, the salts were of the strong base/strong acid, and weak base/strong acid classes, but it is believed that other chemical combinations including salts of the strong base/weak acid, and weak base/weak acid varieties would work equally well. Both the control sizepress solution and the sizepress solutions containing the different salts were prepared in the same manner disclosed for Example 1 except that PG 280 starch, a product of Penick and Ford, Ltd. was used. For the control, a 15% by weight PG 280 starch solution was used to produce control sheets. The remaining size press conditions were comprised of 15% by weight PG 280 starch and 3% by weight of each of the salt materials. The amount of PG 280 starch used was greater than the starch used for the Examples conducted with Pearl X starch to achieve approximately equivalent final viscosities for the sizepress solutions.

TABLE IV Size press Solution l: PG 280 Starch Condition Charge Acceptance Time to (volts) Decay( sec.

Control 600 over 10 3% K SO 700 6-7 371 KNO 700 4-5 371 KCl 600 1-2 3% NH Cl 700 l2 3% NaCl 600 ()l The results of the test data shown in Table IV make it clear that suitable antistatic properties are readily achieved with each of the inorganic salts tested and at a relatively low weight of addition. However, the most efficient salts appear to be those which contain the chloride anion.

EXAMPLE V Later on a production trail of code paper was conducted at the Westvaco Corporation Paper Mill in Tyrone, Pennsylvania (No. 4 Papermachine) during which three different conditions were evaluated. In the first case, an 8.3% by weight Pearl X starch solution was used to produce control sheets. The pickup from this formulation was about 1.5 lb/ream. A second condition comprised 8.3 Pearl X starch and 0.6 potassium chloride (KCl) which produced a pickup of 1.6 lb/ream. And the third trail condition comprised 8.3 Pearl X starch and 0.3% KCl which produced a pickup of about 1.6 lb/ream with all percentages being by weight. The paper thus produced was then dried, cut into sheets and subjected to electrometer tracings substantially as set forth in Example 1 in order to determine the effectiveness of the antistatic agents applied. The results of the tests are reproduced in Table V.

The results of the test data shown in Table V make it clear that for the production of code paper on the papermachine, suitable antistatic properties are readily achieved with the inorganic salt KCl in rather small quantities. The data also shows that the charge acceptance of the null production paper appeared to be lower than the paper treated on the laboratory size press (Examples I, II, and III.). However, it should be noted that different electrometer devices were used to test the sheets prepared in the laboratory and the sheets prepared at the paper mill, and the significant point, vis-a-vis improved antistatic properties, can readily be seen by comparing the performance of the salt impregnated sheets with the control sheets for each Example.

Another test performed on paper samples prepared during the above trail was the Burpee Punch test. For this purpose, the paper samples were conditioned at 20% RH and punched with a Burpee Punch. The Burpee Punch is commonly used to introduce and store information on code paper tapes by punching a sequence of holes in the paper tape. In the past, it was found that code paper which has accumulated a static charge presented problems when punched on the Burpee unit since the chads punched from the paper tended to accumulate and cling to one another. However, based on the results noted in Table I, only the control sheets caused static problems.

EXAMPLE VI In yet another machine trial on No. 4 papermachine at Westvacos Tyrone, Pennsylvania paper mill, two additional size press conditions were used in the manufacture of Westvacos Intra-Lube Code Paper. For this example, the size press formulation fully described in applicantprior US. Pat. No. 3,702,801 was used. Thus the size press solutions for the first condition comprised 8.3 Pearl X starch, 4% Faxam 40 lubricating oil and 0.05 emulsifier Tergitol NP-27 all percentages by weight. In the second condition, everything remained the same except that 0.6 KCl was added to the formulation. The paper made under the above noted conditions was then sheeted and the samples used to prepare electrometer tracings in order to determine the effectiveness of the different treatments. In each case the amount of size press formulation pickup varied from 1.5 to about 1.8 lb/ream. In addition, code paper samples from the two conditions were also subjected to the Burpee Punch test and the visual results were noted. The data obtained from the tests is set forth in Table VI.

TABLE VI Intra-Lube Code Paper Size press Formulation From the above examples it can be seen that an improved process for making antistatic paper has been disclosed. By sizing the paper prepared from chemical pulp with a size press formulation containing only a very small amount of an inorganic salt, the antistatic properties of the paper is improved significantly over paper containing no salt as determined from the elecrometer data. In addition, the introduction of the inorganic salt to the size press formulation either on or off the papermachine does not deleteriously affect the physical properties of the paper, nor does it affect the lubricity of code paper prepared in accordance with the process disclosed in applicants prior US. Pat. No. 3,702,807. On the machine, the salt apparently becomes uniformly distributed throughout the paper before fiber to fiber bonding is complete, and thereby is bonded between the fibers to permit good internal dissipation of the static charges. Thus, when sized on the papermachine, the amount of salt necessary to produce the desired antistatic properties in dramatically low because the salt is more readily dispersed in the paper where fiber-to-fiber bonding is incomplete with an improved ability to become bonded to the more readily available paper making fibers. Off the machine, the aqueous nature of the sizepress solution apparently serves to loosen up the surface of the sheet thereby making available a lesser number of paper making fibers for attracting the salt. Hence a greater salt content is required in the offmachine operation to achieve substantially the same antistatic properties.

Accordingly, even though only several exemplary treatments have been fully disclosed herein, it is delieved that any inorganic salt would serve to produce the results described as long as the ionic species became bonded to the papermaking fiber. Therefor various changes in the invention as disclosed could obviously be made without departing from the invention as a whole, and particularly as defined in the appended claims.

I claim:

1. The process of making antistatic code paper from chemical wood pulp which comprises the steps of:

a. preparing a size press dispersion by dispersing an inorganic salt selected from the group consisting of ammonium chloride, potassium chloride or sodium chloride in an aqueous dispersion of starch to form a sizepress dispersion said sizepress dispersion containing by weight from about 1.5 to 15% starch and from about 0.3 to 6% salt;

b. sizing the paper at a size press with the dispersion to impregnate the paper with an evenly distributed amount of the dispersion ranging from about 0.5 to 2.5 pounds per ream of paper; and

c. drying the paper to permit the salt to become attached to the paper fibers.

2. The process of claim 1 wherein a lubricating oil is present in said dispersion in an amount of l to 10 3. In the process of making antistatic code paper which involves making a web of paper from chemical wood pulp and then sizing the web of paper, the improvement which comprises:

a. preparing a sizepress dispersion consisting of water, starch, lubricating oil and inorganic salt by dispersing an inorganic salt in a aqueous dispersion of starch wherein the starch comprises from about 1.5 to 15% of the weight of the sizepress dispersion and the inorganic salt comprises from about 0.3 to 6% of the weight of the sizepress dispersion;

b. impregnating a traveling web of the paper at a size press on a papermaking machine with the sizepress dispersion before fiber-to-fiber bonding becomes complete, to provide the paper with an evenly distributed amount of the dispersion ranging from about 0.5 to 2.5 pounds per ream of paper; and

c. drying the paper to permit the salt to become bonded to the papermaking fibers.

4. The process of claim 3 wherein the inorganic salt is selected from the group consisting of ammonium chloride, potassium chloride, sodium chloride, potassium sulfate and potassium nitrate.

5. The process of claim 4 wherein said lubricating oil is present in said dispersion in an amount of l to 10 72. 

1. THE PROCESS OF MAKING ANTISTATIC CODE PAPER FROM CHEMICAL WOOD PULP WHICH COMPRISES THE STEPS OF: A. PREPARING A SIZE PRESS DISPERSION BY DISPERSING AN INORGANC SALT SELECTED FROM THE GROUP CONSISTING AMMONIUM CHLORIDE, POTASSIUM CHLORIDE OR SODIUM CHLORIDE IN AN AQUEOUS DISPERSION OF STARCH TO FORM A SIZEPRESS DISPERSION SAID SIZEPRESS DISPERSION CONTINING BY WEIGHT FRON ABOUT 1.5 TO 15% STARCH AND FROM ABOUT .3 TO 6% SALT: B. SIZING THE PAPER AT A SIZE PRESS WITH THE DISPERSION TO IMPREGNATE THE PAPER WITH AN EVENLY DISTRIBUTED AMOUNT OF THE DISPERSION RANGING FROM ABOUT 0.5 TO 2.5 POUNDS PRE REAM OF PAPER: AND C. DRYING THE PAPER TO PERMIT THAT SALT TO BECOME ATTACHED TO THE PAPER FIBERS.
 2. The process of claim 1 wherein a lubricating oil is present in said dispersion in an amount of 1 to 10 % .
 3. In the process of making antistatic code paper which involves making a web of paper from chemical wood pulp and then sizing the web of paper, the improvement which comprises: a. preparing a sizepress dispersion consisting of water, starch, lubricating oil and inorganic salt by dispersing an inorganic salt in a aqueous dispersion of starch wherein the starch comprises from about 1.5 to 15% of the weight of the sizepress dispersion and the inorganic salt comprises from about 0.3 to 6% of the weight of the sizepress dispersion; b. impregnating a traveling web of the paper at a size press on a papermaking machine with the sizepress dispersion before fiber-to-fiber bonding becomes complete, to provide the paper with an evenly distributed amount of the dispersion ranging from about 0.5 to 2.5 pounds per ream of paper; and c. drying the paper to permit the salt to become bonded to the papermaking fibers.
 4. The process of claim 3 wherein the inorganic salt is selected from the group consisting of ammonium chloride, potassium chloride, sodium chloride, potassium sulfate and potassium nitrate.
 5. The process of claim 4 wherein said lubricating oil is present in said dispersion in an amount of 1 to 10 %. 